Alkaline paper differs from acid paper in that some alkaline paper contains internal sizing (added to the wood pulp rather than to surface of the paper), such as, alkyl succinic anhydride (ASA), to prevent rewetting of the paper. However, certain conventional opacifiers such as mixtures of the mono- and di-stearamides of amino ethyl ethanol amine, tend to react with the ASA sizing which prevents the sizing from functioning. As a result, the paper absorbs water.
It would be desirable to have an opacifier for alkaline paper which does not react with alkyl succinic anhydride.
The present invention provides a novel opacifier and opacifying composition for use with alkaline paper which does not react with alkyl succinic anhydride. The opacifier comprises a mixture of: an aromatic polymer, preferably an aromatic acrylic polymer or an aromatic anhydride polymer, more preferably a styrene acrylic polymer or a styrene maleic anhydride polymer; and a stearamide. The stearamide preferably comprises either a mono-stearamide or a di-stearamide of an ethanol amine, more preferably the stearamide comprises both a mono-stearamide and a di-stearamide of an ethanol amine, preferably an amino ethyl ethanol amine. Preferably the opacifier comprises from 5% to 60%, more preferably from 15% to 50%, most preferably from 30% to 40% aromatic polymer and preferably from 40% to 95%, more preferably from 50% to 85%, most preferably from 60% to 70% of the stearamide.
Preferably the opacifying composition comprises from 0.01% to 100%, more preferably from 2 to 50%, even more preferably from 3% to 40%, most preferably from 5% to 35%, opacifier; and from 0% to 99.99%, preferably from 0.001 to 99.99%, more preferably from 50% to 98%, even more preferably from 60% to 97% water; most preferably from 65% to 95% water. The water is preferably present in an effective amount to emulsify the opacifier and thus to provide the opacifying composition in a liquid, emulsion form. A base is preferably present in an effective amount to provide the opacifying composition with a pH greater than 7.5. The base is preferably present in an effective amount to provide the opacifying composition with a pH of from 7.5 to 11.0. In a embodiment where water is employed, the opacifying composition is preferably an emulsion.
When the opacifying composition is added to the alkaline wood pulp, the paper produced therefrom has the desired opacity, brightness and non-absorbency. The inventions also relate to paper, methods of enhancing optical properties of paper and to methods of making the novel opacifying compositions.
The present invention provides a novel opacifying composition for use with alkaline paper which does not react with alkyl succinic anhydride. As used herein, xe2x80x9cpaperxe2x80x9d means a matted or felted sheet of fiber. Preferably the fiber is cellulose. The opacifying composition comprises a mixture of an aromatic polymer, preferably a styrene acrylic polymer, and a stearamide which preferably comprises a mono-stearamide or a di-stearamide of amino ethyl ethanol amine. Most preferably the stearamide comprises both a mono-stearamide or a di-stearamide of amino ethyl ethanol amine. Preferably the opacifier comprises from 5% to 60%, more preferably from 15% to 50% , most preferably from 30% to 40% aromatic polymer and preferably from 40% to 95%, more preferably from 50% to 85%, most preferably from 60% to 70% of the stearamide.
Preferably the opacifying composition comprises from 1% to 100%, more preferably from 2 to 50%, even more preferably from 3% to 40%, most preferably from 5% to 35%, opacifier, and from 0% to 99%, more preferably from 0.001 to 99%, even more preferably from 50% to 98%, most preferably from 60% to 97% water. The water is preferably present in an effective amount to provide the opacifying composition in a liquid, emulsion form. Thus, the opacifying composition may be in solid form comprising primarily the opacifier, or in liquid form comprising water and the opacifier.
A base is preferably present in an effective amount to provide the opacifying composition with a pH greater than 7.5. The base is preferably present in an effective amount to provide the opacifying composition with a pH of from 7.5 to 11.0.
When the opacifying composition is added to the alkaline 25 wood pulp, the paper produced therefrom has the desired opacity, brightness and non-absorbency. As used herein, xe2x80x9calkaline wood pulpxe2x80x9d means the wood pulp has a pH of from 6.5 to 9.0.
The Aromatic Polymer
The aromatic polymer is preferably an aromatic acrylic polymer or an aromatic anyhdride polymer, preferably a styrene acrylic polymer, or a styrene maleic anhydride resin. Preferably the aromatic polymer has a molecular weight of from 500 to 16,500.
The Aromatic Acrylic Polymer
Preferably the aromatic acrylic polymer has a weight average molecular weight of from 4,000 to 16,500 more preferably from 7,000 to 10,000, most preferably from 7,500 to 9,000. Preferably the styrene acrylic polymer has a softening point from 53xc2x0 C. to 300xc2x0 C., more preferably 70xc2x0 C. to 250xc2x0 C., most preferably from 90xc2x0 C. to 185xc2x0 C., an acid number preferably from 40 to 280, more preferably from 100 to 260, most preferably from 150 to 230, a density of preferably from 1.05 to 1.6, more preferably from 1.09 to 1.5, most preferably from 1.1 to 1.2, and a glass transition temperature of preferably from 40xc2x0 C. to 140xc2x0 C., more preferably from 45xc2x0 C. to 130xc2x0 C., most preferably from 65xc2x0 C. to 105xc2x0 C.
Preferably the aromatic acrylic polymer is a styrene acrylic polymer. A suitable styrene acrylic polymer has a weight average molecular weight of 8,000 and is commercially available under the tradename Morez 101 from Morton. A suitable styrene acrylic polymer has a weight average molecular weight of 8,500, an acid number of 215, a softening point of 165xc2x0 C., a glass transition temperature of 85xc2x0 C., and a density of 1.13 and is commercially available under the trade name Joncryl 678 from Johnson Polymer.
The Aromatic Anhydride Resin
The aromatic anyhdride resin preferably has a weight average molecular weight of 500 to 10,000. The aromatic anhydride resin is a copolymer of a substituted aromatic ring and an anhydride, preferably a copolymer of styrene and maleic anhydride and the esters and salts thereof, preferably having aromatic:anhydride ratio of from 1 to 3:1. Preferably the aromatic anhydride has a melting point range of from 45-180xc2x0 C., more preferably 100-175xc2x0 C., most preferably from 150-170xc2x0 C. Preferably the aromatic anhydride has an acid number of from 100 to 500, more preferably from 106 to 490, most preferably from 350 to 485 and preferably a 15% NVM viscosity of from 10 to 60, more preferably 12 to 26, most preferably 15 to 20 cP at 30xc2x0 C.
Preferably the aromatic anhydride resin is a styrene maleic anhydride resin. A suitable styrene maleic anhydride resin is a styrene maleic anhydride copolymer, having a weight average molecular weight of 8,000, a melting point range of 150-170xc2x0 C., and acid number of 480 a 15% NVM viscosity of 17 cP at 30xc2x0 C. and a styrene: maleic anhydride ratio of 1:1, a Gardner color of 1-2, and is commercially available under the trade name SMA(copyright) 1000 from Atochem North America Inc.
The Stearamide
The stearamide has the following general structure: 
wherein:
m is an integer from 0-1;
n is either an integer from 11 to 23; preferably from 15 to 17;
o is an integer from 0-1;
R1 is a hydrogen;
R2 is an alkyl group having from 1 to 15 carbon atoms preferably 2 to 6 carbon atoms;
R3 is an aliphatic alcohol group having from 1 to 15 carbon atoms preferably 2 to 6 carbon atoms;
and R4 is 
wherein p is an integer from 11 to 23, preferably 15 to 17.
Preferably the stearamide comprises either a monostearamide or a di-stearamide or a mixture of both. Preferably the stearamide comprises from 1% to 50%, more preferably from 10% to 30% of at least one mono-stearamide; and from 50% to 99%, more preferably from 70% to 90% of at least one di-stearamide. Preferably the mono-stearamide is a mono-stearamide of amino ethyl ethanol amine and has the following formula: 
Preferably. the di-stearamide of amino ethyl ethanol amine has the following formula: 
A suitable stearamide is a mixture of the mono-stearamide a the di-stearamide of the amino ethyl ethanol amine and is commercially available under the trademark, Reactopaque(copyright) from Omnova Solutions Inc. formerly GenCorp.
Suitable bis-stearamide ethoxylates are for example, methylbis-(tallowamidoethyl)-2-hydroxyethyl ammonium methyl sulfates and esters thereof, are commercially available under the trademarks, Accosoft(copyright) and Stepanix(copyright); particularly suitable is The Accosoft(copyright) 550, from the Stepan Company.
Optionally, the opacifying composition further comprises an alkyl alcohol ether to stabilize the emulsion of the opacifying composition. Dipropylene glycol methyl ether is the preferred.
Optionally, the opacifying composition further comprises an emulsifier to promote homogeneity. Conventional emulsifiers are suitable. Good results have been obtained using 5% of a nonyl phenol with 40 moles of ethylene oxide emulsifier commercially available under the trade name Triton x-405 from Rohm and Haas.
Preparation of the Opacifying Composition
Preferably, the opacifying composition is prepared by heating the stearamide under an inert atmosphere with agitation. Good results have been obtained by heating to 125xc2x0 C. The aromatic polymer is then added and mixed; good results have been obtained by mixing for one hour. The opacifying composition is then preferably cooled. The opacifying composition is then combined with water and a base preferably ammonia, and then heated until the base is solubilized. Good results have been obtained by heating to 90xc2x0 C.
The emulsified form of the opacifying composition is formed by adding water which contains a base, such as ammonia, sodium hydroxide, monoethanolamine, diethanolamine, triethanolamine, or potassium hydroxide, and heating with agitation. Good results have been obtained by heating at 90xc2x0 C. for 60 minutes or until the opacifying composition is solubilized.
The opacifying composition is added to a pulp slurry, also known in the art as a xe2x80x9cfurnishxe2x80x9d, which then is used to form a paper sheet. The pulp slurry is made using conventional techniques. The pulp slurry contains typically cellulose fiber derived from hardwood or soft wood or a mixture of the two.
After the pulp slurry is formed, it is stored in holding tanks or fed into a papermaking machine. The opacifying composition is added to the pulp slurry after the pulp has been bleached, but before the pulp enters the head box of the paper making machine. The opacifying composition is added to the slurry when the pulp slurry is in the holding tank or is added to the pulp slurry as it moves along to the headbox of the papermaking machine. The opacifying composition is added preferably from 0.1 to 15 pounds/ton, more preferably from 0.5 to 12 pounds/ton, even more preferably from 1 to 7 pounds/ton, most preferably from 2 to 4 pounds/ton of pulp slurry.
The paper made from the pulp slurry containing the opacifying composition is made using conventional techniques.
The Paper
The paper of the present invention comprises cellulose fibers; an aromatic polymer; and a stearamide. As used herein, xe2x80x9cpaperxe2x80x9d means all types of sheets containing cellulosic fiber and includes but is not limited to, tissue, toweling, cardboard, newsprint, fine paper, lightweight coated paper, bible grade phone book grade, super calendar grade, liner board, reply card grade, cylinder board, super calendar grade, and filled sheets. The amount of opacifier present on the paper is preferably from 0.0 001% to 10%; more preferably from 0.01% to 5%, most preferably from 0.05% to 2%.